This invention relates to the manufacture and structure of a radio frequency antenna, specifically one for use in a compact array.
An antenna radiates or receives energy. A radio frequency (RF) antenna for use in a microwave radar radiates or receives energy in the radio frequency range that is typically 1-20 GHz (gigahertz), but may be higher or lower. The RF antenna may be structured to radiate or receive energy over a broad bandwidth or a narrow bandwidth. RF antennas are widely used in military applications such as aircraft and missile guidance.
In a compact antenna array, the RF energy needed to excite the individual radiating elements originates from a single transmitter. The energy is then distributed to all the elements through the antenna feed network. To have the antenna operate across a wide instantaneous bandwidth, the feed network often uses a corporate architecture with matched four port power dividers (one port is terminated in a matched load) performing the RF power distribution. Such corporate feed structures are well known in the art.
A number of designs of RF antennas are also well known. Many are based upon microwave waveguide principles, in which a waveguide directs energy in a selected direction and radiates the energy outwardly into free space (or equivalently, receives energy radiated through free space).
The radiating elements may include conventional waveguides, waveguide horns, and various other forms. In most applications, the operational bandwidth of a waveguide or waveguide horn is considered to be the range of electromagnetic waves that can propagate within the waveguide as a single fundamental mode or a pair of orthogonal fundamental modes. The addition of conductive ridges in the walls of a waveguide (typically referred to as a “ridged waveguide” or RWG) is known to increase the bandwidth of the waveguide.
The principal known techniques for fabricating RF antennas include foil forming, dip brazing, and electroforming of metallic-based structures. Individual antenna elements are fastened to the feed structure by mechanical fasteners, adhesives, or solders. Mechanical fasteners are time-consuming to install. Adhesives typically require careful application and curing at elevated temperature for an extended period of time. Solders are sometimes difficult to use, especially when there is an attempt to achieve precision alignment of soldered structures. Additionally, all of these techniques result in a relatively heavy antenna structure, which is undesirable in a flight-worthy vehicle.
A typical compact antenna design, such as that used in seekers, direction finding, or aircraft, strives to accomplish are high gain, large bandwidth, ease of manufacturability and low cost. Current state of the art struggles to accomplish all of the above in one design. One prior art example of a solution to this problem is found in U.S. Pat. No. 6,052,889, to Yu, et al., (Yu '889) incorporated herein by reference in its entirety. In that apparatus, the inventors addressed the problems by fabricating the antenna elements by first injection molding a group of broadband radio frequency radiating elements from a polymeric material, metalizing each broadband radio frequency radiating element, and installing a transmission line within each broadband radio frequency radiating element. While this design provides excellent performance, it requires a complicated manufacturing process.
Thus, there is a need for an improved approach to the design and fabrication of RF antennas that reduces both cost and weight of the antenna, and is compatible with either broadband or narrow band applications.